Achieving crop fertilization by timing the release or application of fertilizer nutrients is known. Fertilization in the container-grown wholesale plant industry, for example, has been accomplished by methods including:                Multiple applications of granular fertilizer        Overhead liquid application of soluble fertilizers        Incorporating slow release fertilizers into potting soil        Polymer coated fertilizers.        
Each of these methods and compositions has associated drawbacks. A description of the drawbacks associated with prior art methods and compositions can be found in U.S. patent application Ser. No. 10/973,732, which is incorporated in its entirety herein.
Encapsulating fertilizers to slowly release nutrient to plants is known. Slow release fertilizers delay the dissolution of the fertilizer substrate. Most slow release fertilizers, however, are not dependable in adverse environmental conditions such as high heat and moisture. Hot and wet conditions can cause slow release fertilizers to flash release, causing damage to both the plant material and the environment.
Prior art methods include encapsulating a fertilizer having a given chemical composition or compound such that the nutrients are released over a period of time. For example, coated urea has been used as a source of time released nitrogen, which is a nutrient that promotes plant height and leaf formation in a plant. U.S. Pat. Nos. 5,147,442, 5,560,768 and 6,500,223 each of which is incorporated in its entirety, illustrate such coated fertilizers and methods associated with them.
Encapsulated slow-release fertilizers may be classified into two major groups according to the fertilizer release mechanism:
(i) A first group in which the release is governed by the rate of water permeation through a polymeric or copolymeric membrane of the water-proofing material, and by the rate of fertilizer diffusion away from each coated particle into the surrounding soil. Typical examples of membrane material in slow-release fertilizers of this group are copolymers or glyceryl esters of unsaturated acids with dicyclopentadiene (U.S. Pat. No. 3,223,518), epoxy-polyester resins (U.S. Pat. No. 3,259,482), urethanes (U.S. Pat. No. 3,264,089) and polystyrenes (U.S. Pat. No. 3,158,462).
(ii) A second group with relatively thick encapsulating coats, in which release is governed mainly by rupture of the coat, a typical example being particulate fertilizers with sulfur based encapsulation. The rupture occurs upon the permeation of water into the coated particles as a result of the osmotic pressure that builds up within. The sulfur based coating in slow-release fertilizers of this second group are generally produced by spraying onto the particulate fertilizer a molten sulfur based material as disclosed, for example, in U.S. Pat. No. 4,857,098.
Inefficient fertilization using past existing polymer coated fertilizers described at (i) and (ii) above increases costs and losses with respect to crops. In order to achieve the safe release of nutrient, current slow-release coated fertilizers must be relatively thickly coated, as measured by percentages of weight. Thicker coatings are necessarily more costly as result of, inter alia, the need for more coating materials. What is needed is an encapsulated slow-release fertilizer that can safely release nutrient to plants using coating that is more efficient.